Ring laser gyrocopes based on the Sagnac effect are commonly used in many modem navigational and aerospace guidance systems. In summary, two light beams are caused to propagate in opposite directions around a closed-loop path. Rotation of this closed loop path causes the effective path length in one direction to become shorter while lengthening the effective path length in the other direction. This change in path length is a direct measure of inertial rotation. Further details regarding the general operation of a ring laser gyroscope may be found in U.S. Pat. No. 3,373,650, by J. E. Killpatrick.
The two most widely used versions for both civilian and military applications are the Ring Laser Gyroscope (RLG), and the Interferometric Fiber Optic Gyroscope (IFOG). While these are proven devices, there are limitations to the reduction in size and cost achievable with these devices. Both systems are based on the construction of relatively long closed paths that are difficult to manufacture and require a relatively large area (see for instance, the review by D. Z. Anderson in Scientific American, vol 254, #4, p. 94, April 1986). A gyroscope based on integrated solid state designs would be an attractive alternative to fiber-optic systems in terms of cost and manufacturablility, and ruggedness of design. One example is an integrated planar optical waveguide approach to a compact gyroscope as described by Ford, et al. in IEEE 2000, p. 285-290.
In recent years integrated semiconductor ring lasers of very small size have been developed. Micro-ring cavity lasers and various means to construct them are discussed by Ho, et al. in U.S. Pat. No. 5,790,583 entitled xe2x80x9cPhotonic-Well Microcavity Light Emitting Devicesxe2x80x9d and U.S. Pat. No. 5,825,799 entitled xe2x80x9cMicrocavity Semiconductor Laserxe2x80x9d and by Jezierski, et al. in IEE Proceedings, Vol. 135, Pt. J, No. 1, p. 17-24, February 1988. More recently a semiconductor ring laser in combination with a fiber-optic loop has been characterized in the context of an optical gyroscope by Taguchi, et al. in Optical and Quantum Electronics vol. 31: 1219-1226, 1999. In this study it was verified that lock-in phenomenon was one of the most dominant noise sources.
Lock-in is a common error source in ring laser gyroscopes which has been an issue for many years. As disclosed by Killpatrick above, when the ring laser gyroscope sits at rest, or is subjected to zero input rates, the two counter-propagating waves tend to resonate together or xe2x80x9clock-inxe2x80x9d. This tendency to lock-in reduces the gyroscopes""s ability to measure rotation at low rates. To alleviate the problem of lock-in, electronic biasing that results in the ring laser gyroscope being rotationally oscillated, was developed as described, for instance, by L. W. Priddy in U.S. Pat. No. 5,774,216 entitled xe2x80x9cRLG Dither Noise Injection by Means of Reference Modulationxe2x80x9d
To date there is no micro-ring cavity laser gyroscope that adequately addresses the issue of lock-in and allows a micro-ring cavity laser based gyroscope to perform at low rates of rotation.
The invention embodies a micro-ring cavity gyroscope with a sensitivity axis, for sensing rotational motion, comprising: at least one micro-ring cavity laser comprising a light amplifying medium and magneto-optical material capable of generating an electromagnetic standing wave; at least one standing wave detection means; and means for generating a magnetic field that at least partially immerses said micro-ring cavity laser in magnetic field, wherein said standing wave detection means senses the position of the electromagnetic standing wave with respect to said micro-ring cavity laser, and the magnetic field perturbs the electromagnetic standing wave to minimize lock-in phenomenon enabling detection of rotational motion.
The invention further embodies a novel process for changing the effective optical path length of an electromagnetic wave in a magneto-optical material comprising: applying a magnetic field to said magneto-optical material; propagating said electromagnetic wave through the magneto-optical material such that the electric component of the electromagnetic wave has a component perpendicular to the magnetic field; and changing direction of propagation of the electromagnetic wave such that a projection of the propagation direction is perpendicular to the magnetic field whereby the effective optical path length is modified.